The present invention relates to compositions for removing etch residue and methods for their use, particularly in semiconductor device fabrication.
In the fabrication of semiconductor integrated circuits (ICs), various layers of inorganic material form semiconductor-based substrates. Some of the inorganic layers are patterned in desired shapes. The resulting inorganic layers form individual devices and interconnect structures within the IC.
Patterning conventionally includes masking an underlying layer with an organic resist material (i.e., mask), such as photoresist, exposing the resist, and removing exposed areas of the mask to form a patterned mask layer. The exposed inorganic layer underlying the patterned mask layer is then removed using an appropriate etchant. The patterned mask layer is then removed.
Etching is a process for removing unwanted material (i.e., partial or complete layers of material) from a surface (e.g., the surface of a semiconductor-based substrate). Organic or inorganic material, which may be patterned or unpatterned, of a substrate surface can be removed using an etching technique. Ideally, etching should precisely remove material that is not covered by a patterned mask layer (i.e., material that is xe2x80x9cexposedxe2x80x9d when a patterned mask layer is used).
The etchant is typically chemically varied according to the type of material being etched. Etchants are characterized as isotropic or anisotropic and further characterized as being selective or nonselective, depending on their ability to differentiate between material that they effectively etch. Selective etchants remove different types of material at different rates. Isotropic etchants remove material in all directions at the same rate.
Etching can occur in a wet or dry processing environment. Wet etching refers to the contact of a substrate surface with a liquid chemical etchant. Material is removed as an agitated liquid or spray, for example, passes over the substrate surface. Dry etching refers to the contact of a substrate surface with a gaseous plasma etchant. Wet etching is preferred over dry etching due to its ability to provide high, reliable throughput with excellent selectivity. Many wet etching compositions include water, however. When such aqueous compositions are used, they can cause problems with respect to corrosion, particularly corrosion of underlying metal layers. Corrosion inhibitors, such as catechol and pyrogallol, are typically used in aqueous etching compositions to reduce the corrosive nature of such etchants. Such compositions, however, can be toxic and require special handling precautions.
Commonly used wet etchants are hot alkaline etchants or acidic hydrogen peroxide (H2O2) etchants, which have a significant water content. Typically, alkaline solutions remove organic films, while acidic solutions remove alkali ions, alkali compounds, and other metallic contaminants. For wet etching silicon (Si), mixtures of nitric acid (HNO3) and hydrofluoric acid (HF) are typically used. For wet etching silicon dioxide (SiO2) or other oxides, various HF solutions are typically used, usually further containing a buffering agent to prevent depletion of fluoride ions from the etchant during etching. Silicon nitride (Si3N4) is typically wet-etched using a hot phosphoric acid (H3PO4) solution. Aluminum (Al) is typically wet-etched using a mixture of phosphoric acid (H3PO4), acetic acid (CH3COOH), nitric acid (HNO3), and water (H2O).
Dilute HF and buffered oxide etchant (BOE), which is a dilute mixture of HF and ammonium fluoride (NH4F), usually in a ratio of about 1 part HF to 6 parts NH4F (by volume), are prevalent conventional SiO2 etchants. Both dilute HF and BOE are typically diluted in water in a ratio of about 10:1, 20:1, or 100:1 (i.e., 10, 20, or 100 parts (by volume) of water to one part reactive etchant components). Another conventional aqueous etchant, sold by Olin Hunt in Chandler, Ariz. that has been used to etch oxide is referred to as xe2x80x9cSUPER Q,xe2x80x9d which is a mixture of NH4F and phosphoric acid (H3PO4).
Both wet and dry etching can leave an etch residue, although the residue is more dramatic for dry etching, which typically leaves a polymeric residue. This polymeric etch residue is a necessary component for achieving anisotropic etching. It typically includes halogenated organic compounds with inorganic material dispersed throughout and typically must be removed prior to subsequent processing. For example, etch residue may be a polymeric residue including tantalum, titanium, chlorine, and carbon therein when layers such as titanium nitride and tantalum pentoxide are patterned using photoresist and a chlorine-containing plasma etchant. If the etch residue is not effectively removed, various operating failures may occur. For example, conductive etch residue may cause a short between the first and second electrodes of a capacitor structure. Nonconductive etch residue may effect critical dimensions and adhesion of subsequent layers.
Various aqueous cleaning solutions are available for cleaning etch residue from semiconductor-based structures. For example, an SC1 clean, an SC2 clean, a piranha clean, a buffered oxide etch solution, and other fluorine-containing aqueous-based chemistries have been used for cleaning residues-from structures. However, such cleaning solutions are not effective at removing etch residue from a wide variety of semiconductor structures, such as vias. Such cleaning solutions typically fail to clean the etch residues without attacking the desired structures. These solutions also typically have the problem that they also attack and dissolve aluminum. Thus, these cannot be used to remove etch residue after aluminum patterning steps.
One commercially available cleaning composition does not typically attack aluminum; however, it does not remove etch residue at a very effective rate. This solution includes NH4F in a polyhydric alcohol. Thus, what is needed are cleaning compositions that effectively remove etch residue, such as polymeric dry etch residue, but do not typically attack desirable materials on semiconductor devices, such as aluminum, for example.
The present invention provides a composition useful for cleaning (i.e., removing etch residue from) etched substrates such as semiconductor device structures. The compositions of the present invention include one or more fluoride ion sources and one or more organic solvents. Significantly, because compositions of the present invention typically include one or more organic solvents and no greater than about 3 wt-% water, there is less attack on aluminum patterned features, even when compositions contain relatively high concentrations of fluoride ions.
Specifically, the present invention provides a method of removing etch residue from a substrate (preferably, a semiconductor structure), the method comprising: providing a composition comprising at least one fluoride ion source comprising an organic cation and at least one organic solvent; providing a substrate having etch residue on at least one surface; and contacting the surface of the substrate having etch residue thereon with the composition under conditions effective to remove at least a portion of the etch residue. The step of contacting the surface of the substrate may include immersing the substrate in the composition, spraying the surface of the substrate with the composition, or both.
In another embodiment, the present invention provides a cleaning method in a semiconductor fabrication process, the method comprising: providing a semiconductor structure having an etch residue on at least a portion thereof; providing a composition comprising at least one fluoride ion source comprising an organic cation and at least one organic solvent; and exposing the semiconductor structure to the composition to remove at least a portion of the etch residue. Preferably, the semiconductor structure comprises a via. Typically, the etch residue is present on the sidewalls of the via (0.6 micron diameter).
In another embodiment, the present invention provides a cleaning method in a semiconductor fabrication process, the method comprising: providing a semiconductor structure having an etch residue on at least a portion thereof; providing a composition comprising greater than about 1.0 wt-% of at least one fluoride ion source comprising an organic cation and at least one organic solvent; and exposing the semiconductor structure to the composition to remove at least a portion of the etch residue.
In yet another embodiment, the present invention provides a cleaning method in a semiconductor fabrication process, the method comprising: providing a semiconductor structure having an etch residue on at least a portion thereof; providing a composition consisting essentially of at least one fluoride ion source comprising an organic cation and at least one organic solvent; and exposing the semiconductor structure to the composition to remove at least a portion of the etch residue.
In still another method, the present invention provides a cleaning method in a semiconductor fabrication process, the method comprising: providing a semiconductor structure having an etch residue on at least a portion thereof and comprising a layer comprising at least a portion of exposed metal (preferably, aluminum); providing a composition comprising at least one fluoride ion source comprising an organic cation, and at least one organic solvent; and exposing the semiconductor structure to the composition to remove at least a portion of the etch residue and substantially none of the exposed metal, (preferably at 40xc2x0 C. in an exposure time of no greater than about 5 minutes).
The present invention also provides a composition for use in integrated circuit fabrication, the composition consisting of greater than about 1.0 wt-% of at least one fluoride ion source comprising an organic cation and at least one organic solvent.